1. Field of the Invention
This invention relates in general to electrical switchgear servicing equipment and more particularly to a remotely operated system for circuit breaker operation and for racking circuit breakers into and out of engagement with the primary and secondary disconnect terminals within the electric switchgear.
2. Description of the Prior Art
It is well known in the power distribution industry that personnel who work on or near energized electrical equipment can be seriously injured or killed as a result of arcing faults. An arcing fault is the flow of current through the air between phase conductors and neutral or ground and can result in a tremendous release of energy in the form of extremely high temperatures and pressures along with shrapnel hurling through the air at high velocity. For this reason, when repair work or periodic maintenance needs to be accomplished on medium-voltage switchgear cells and/or on the associated circuit breakers, the circuit breakers are tripped (opened) and moved out of conductive contact with the primary and secondary disconnects and removed from the switchgear cell. Such operations of the circuit breakers is referred to in the industry as xe2x80x9cracking-outxe2x80x9d, and reinstallation is referred to as xe2x80x9cracking-inxe2x80x9d. In some medium-voltage switchgear equipment, racking the circuit breaker out is accomplished by horizontally moving the circuit breaker within the switchgear cabinet which disconnects the circuit breaker from the switchgear power terminals enabling its removal from the cabinet. In another type of switchgear configuration, racking-out is accomplished by vertically lowering the circuit breaker to disengage it from the switchgear power terminals and subsequently moving it horizontally out of the cabinet. The racking-in of this type of equipment is accomplished by horizontally moving the circuit breaker back into the cabinet and elevating it into conductive contact the switchgear power terminals. The present invention is intended for use with the latter type of switchgear equipment, thus this discussion of the prior art will be directed to that type of equipment.
In the absence of any specialized racking equipment, a racking-out operation in this type of a switchgear cell is accomplished by opening the cell-cabinet door to gain access to a circuit-breaker control switch and a racking-motor platform provided in the cell cabinet. The circuit-breaker control switch is used to trip (open) the circuit breaker, and a portable electric motor is mounted on the racking-motor platform. The drive member of the electric motor engages a slide-clutch driven member of the circuit-breaker elevating mechanism to form a coupling and a slide-clutch lever is manually operated to lock the coupled members together. A toggle switch that is located adjacent the racking motor, is then used to run it in a direction which causes the circuit-breaker elevating mechanism to lower the circuit breaker, and when lowered, it can be wheeled out of the cell cabinet. When the maintenance work is finished, the circuit breaker is wheeled back into the cell cabinet and the toggle switch is used to run the motor in the reverse direction to operate the circuit-breaker elevating mechanism to raise the circuit breaker back into conductive contact with the switchgear power terminals. The portable motor is then removed and a circuit-breaker control switch provided on in the cell cabinet door is used to close the circuit breaker. It will be appreciated from the above, that the cell-cabinet door must be open and a worker must be in very close proximity to the equipment to accomplish opening and closing of the circuit breaker and the racking-out and racking-in operations. Thus, the worker is well within the arc-flash danger zone and could be seriously injured or killed in the event of an arc fault. Therefore, it is preferred that some sort of remotely operated mechanism be used to accomplish the circuit-breaker control and racking operations.
Remote racking systems provided by manufactures such as General Electric, Westinghouse, Square D and Siemens are available and some of these systems will only work on the horizontally racked circuit breakers of the switchgear cells discussed above. The prior art remote racking systems that are capable of vertically racking the second type of switchgear cells do provide some worker safety benefits. Workers can perform the racking-in and racking-out operations from a safe distance, however, they must still reach into the cell cabinet to trip and reset the circuit breaker and the cell cabinet doors must be open during the racking operations. A remote racking system which was recently introduced by General electric does allow the cell cabinet door to be closed during the racking operations. However, the worker must still stand in front of the open cell cabinet door to accomplish the tripping, charging and closing functions of the circuit breaker.
In addition, the circuit breakers in the vertically racked type of switchgear cells must remain level during vertical movement. If excessive deviation in the normally level attitude of the circuit breaker should happen because of elevating equipment malfunction, considerable damage due to misalignment of the switchgear and circuit-breaker terminals can result and can cause an arc fault. It is very difficult, if not impossible, for a worker standing off to the side of the cell at a distance of twenty five or thirty feet to detect tilting of a circuit breaker in time to prevent equipment damage and a resulting arc fault. The prior art remote racking systems make no provisions for monitoring the inclination of circuit breakers during racking operations and interrupting racking motor operation upon detection of an irregular tilt angle. Therefore a need exists for a new and improved remote circuit breaker control and racking system for use on switchgear cells of the type requiring vertical movement for racking-out and racking-in of the circuit breakers.
In accordance with the present invention, switchgear cells are modified to include an inclinometer for monitoring the attitude of the circuit breaker, and a solenoid operated latching device interacts with a keyed slide-clutch lever for releaseably interconnecting a portable drive motor and the circuit-breaker racking mechanism. A power transfer panel is mounted inside the cell cabinet for transferring control of the circuit breaker and racking operations to a location external of the cell cabinet. A remote control and status-indicating device is demountably coupled through the cell cabinet to the power transfer panel to allow a worker to accomplish the circuit breaker control and racking operations from a remote location and be advised of the status of the operations taking place within the closed cabinet.
The inclinometer is mounted in any convenient location on the circuit breaker and is a dual-axis monitoring device which automatically measures and sets a xe2x80x9crelative zeroxe2x80x9d reference and will sense angular deviations in the fore-and-aft and lateral attitudes. Upon sensing an excessive angular deviation, which is indicative of a malfunction in the circuit breaker elevating mechanism, the inclinometer will display axis trip angles and provide local and remote visual alarm signals and will automatically interrupt operation of the circuit-breaker elevating mechanism drive motor.
Due to the relatively infrequent need for performing racking operations on switchgear cells and the relatively high cost of racking drive motors, it is a common practice to use a portable motor which is installed in a cell on an as needed basis. When a drive motor is installed in a switchgear cell that is modified in accordance with the present invention, it is clamped in place and the worker operates a special lever mechanism to move a slide-clutch driven member of the elevating mechanism into engagement with the drive member of the motor. A latch key is mounted on the lever mechanism and is movable with the lever into engagement with a latching solenoid to hold the drive and driven members in locked engagement with each other. Upon completion of the racking operation, the worker actuates the latching solenoid from the remote location to disengage the drive and driven members.
As previously mentioned, the power transfer panel transfers control of each circuit breaker control function and the racking functions to the remote control and status-indicating device located externally of the switchgear cell. The power transfer panel is electrically connected to the circuit breaker trip and close circuits, a plug-in junction box which interfaces the existing control power and limit switches, the elevator drive motor, the solenoid operated latching mechanism and the inclinometer. A cable extends from the power transfer panel to a connector mounted in the door of the cell cabinet so that the remote control device can be coupled through the closed cell door during circuit breaker control and racking operations. The remote control device is attachable to the door mounted connector by an elongated cable which allows it to be moved to a safe location away from the cell. The remote control and status-indicating device is configured to allow the worker to remotely control each electrically operated circuit breaker function and all the racking operations and provide the worker with visual indications of the status of all of the operations.